Where is Physics in Your
World??
Mr. Ed Pascuzzi - The
Physics Teacher
Glen Cove High School, Glen Cove, NY 11542
Drop me a Note!
Page last updated:
14 September, 2005 19:05
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bottom for the Navigation Menu)
Enjoy our journey as we discover
the presence of Physics in our
everyday lives and how it assists us in many ways. Scroll through this page
to find answers to the questions in the picture captions on the Physics homepage.
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If the students hold
the Van de Graaf generator before it is turned on (and they stand on a plastic bucket
to remain insulated), they acquire the negative charge of the generator ball and
thus don't receive a shock.
When this happens, because like charges repel, negative charges they've gained all
over their bodies try to
move further and further from each other, thus causing their hair to stand on end
(essentially, the hair is
repelling itself!). If they separate hands while the generator is still
running, they keep the charge they had,
and can thus shock someone, unless they jump off the bucket. Upon jumping
down, nearly all the excess
charge is "grounded" or transferred to the floor, and so, their hair will
quickly flatten out so they can't walk
around school and jolt people after all (sorry girls, I know that would be fun)!
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The
trick to taking these photos is really pretty easy. Essentially, I use a trigger
circuit which "hears" the
pop and then causes the flash to go off in a darkened
room with the SLR camera on the "bulb" setting. If
the balloon rip is pretty slow compared to the time
it takes the flash to respond to the pop sound, I can thus
capture the rip in progress (although, if you vary
the distance from the trigger to the balloon you can also
change the amount of
"rip" you capture). To find the rip speed, you need the rip
distance and the rip time
(because speed = distance/time). The distance is just the
length of the balloon (about 12 inches or 30 cm)
and the rip time is about 20 milliseconds, so dividing
the two gives a speed of 600 inches/sec (or
1500 cm/sec). In "regular" terms, this is about 50
feet/sec, or about 34 miles per hour. Stand back!
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Nearly
every sport is a great example of many physics principles in action (except golf, of course..ha
ha! just kidding). Before you answer the question, you can think
about it to help get the answer. The whole
point of kicking the ball is to get it to travel as far as possible,
and so the only way to do that is to give the
ball a great speed (or momentum). To do that,
the kicker must
put his entire body into the kick (called a
"follow-through"), which yields the
greatest possible force exerted on the ball that his body can give.
The
product of this force and the time over which it acts is called an
"impulse" and the greater the impulse
imparted to the ball, the greater the change of momentum of the ball, and thus...it
goes pretty far downfield.
So, if the kicker did not run several yards before kicking the ball, it simply
would not go far. Other sports
which include the follow-through for maximum ball speed include; baseball
(pitching), golf (in the swing),
shotputting, tennis (in the serve), lacrosse and karate, to name a few.
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This is a really cool shot! It's tough to get a good eclipse picture without lugging
around lots of heavy,
delicate and expensive equipment, but it's well worth it.
Here, the camera body was attached to the end of
4 inch apochromatic refracting telescope which was attached to a
motor that allowed the entire scope to track
the Sun (to compensate for Earth's rotation). In
the
image, you can clearly see the magnetic field lines of the
Sun because the particles in the corona (which make up
the
"solar wind") have either - or + charges to them.
Well, in electromagnetism, it's a well known observed fact that
a
moving particle that has a charge experiences
a force when there's a magnet around, and thus
these coronal
particles trace
the magnetic field of the Sun. In
class, we do the same thing using a dash of iron shavings
sprinkled
on top of
a magnet
(pass
the salt please!).
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I'm sure not one of us out
there hasn't seen a rainbow, but if you haven't, just make one! Head
outside on a sunny warm day and shoot a fine mist of water into the
air from your garden hose, but be sure that
the Sun is to
your back and not facing you. As
you peer through the water mist, you should easily see a rainbow,
just as you see in
the above images. What's
happening is that as sunlight strikes the water droplets, different
colors of the light travel in
the water droplets at
different speeds (because each color has a slightly different
index of refraction, which simply means
that, believe
it or not, different colors change the optical density of the water).
As a result,
the sunlight's colors become more pronounced and separate into individual
beams of color (called
dispersion) within the drop. Now, because the drop
has reflective properties, these colors bounce off the
inner droplet walls until they exit, and thus, you see the rainbow.
Notice
that you always see the rainbow
OPPOSITE the location of the Sun in the sky, and that red is on the
top
(it turns out that because the red light
travels a bit faster than the blue light, it suffers less refraction, or passes
through the drops with less change in
its direction). So, to answer the question, a single color laser could not
show this effect, because a single color
is not made of many colors of the spectrum and can't be dispersed as white light
can be. This is how Isaac
Newton proved sunlight was made of component colors that we call
"ROYGBIV"-the abbreviations of the words
for the colors we see in the spectrum.
Now, check out the Glory photo! This is tough to
see, but its out there. The next time you are on a flight,
above the clouds, try to spot this on a side of the plane away from
the Sun. It is essentially a rainbow too, but
since it's not cut
off by the Earth, it's a full circle and not just
an arc. For more details, see
the article I wrote
in the March 1998 issue of The Physics Teacher magazine (Vol. 36, #3, pg. 164).
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I actually got these photos by chance, and was trying to capture something tougher to get
on film, called
the "green flash." Unfortunately, that didn't happen, but I think these
are actually more interesting. An entire
roll of film was shot through a portable 4
inch f/11
Catadioptric telescope from the Sunset
Motel in Greenport,
NY, on the beach overlooking Long Island Sound, such that the setting Sun was
visible directly over the water
(and of course, it was a super clear day). Essentially, there are
several things happening. First, notice that the
Sun is flattened horizontally (not vertically) because layers of our
air change temperature and pressure vertically,
and as a result, the index of refraction
of the air
changes in that direction. Thus, the air acts like many many
different tiny lenses, distorting the image of the
Sun
so it does not look spherical near the horizon. Also,
notice the "AntiSun" rising to meeting the true
Sun as
the actual Sun sets. This is also a lensing effect of our
air, and this AntiSun is actually an inverted (real) image
of the
true setting Sun (sort of analogous to a "mirage"
you see on a long road on a hot day).
In fact, by the time
the top image of the AntiSun is seen, the bottom
limb of the true Sun is actually below the horizon!
So, in a
sense, these lensing effects, if you
think about it,
actually change the length of the day, because the sunrise and
sunset
times must be corrected for when the
limb is really below the horizon. Very cool!
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Another unusual shot from Maho Beach on St. Maarten in the Netherlands
Antilles, where the runway at
Princess Juliana Airport ends right where the beach begins. As
jets descend on approach, they obviously must
slow down in a controlled manner, and in doing so, must also descend
gradually. Since it is the air that keeps
the plane aloft (yes, that's all that holds these behemoths
up!), the plane must also make use of the air to reduce
its speed, but still keep it from falling too quickly. Thus,
the way to do this is simply change the shape of the
wing, which is done using leading edge slats and trailing edge
flaps. Doing so not only increases the area of the
wing (and thus the amount of lift while it
slows down) but also
creates more forward drag due to air resistance,
which helps slow the plane to a safe landing speed.
So, is the
plane in static or dynamic equilibrium? Since it
must be slowing down, it is in neither situation! There is a
slight
net force on the jet, and so it must be
decelerating. Either way, it's pretty wild seeing these monster jets coming
at me while I'm soaking up the
sunshine!
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It's
just not possible to not have fun at Six
Flags Great Adventure on Physics Day! There is something here
for everyone (even Waffle Cones!). On Physics Day, students
have many activities to do to determine speeds,
momenta, energies and other
goodies as they plummet to Earth on a variety of chilling rides. Here, on
Stuntman's Freefall, people sit and plummet toward the ground in a
small car on a track some 100 feet
(30 m) above the heads of onlookers. Of course,
to help them return to the ride (and thus...survive!), the car
must be decelerated
rapidly, thus the need for the curved track. As a result, only a very
small portion of the ride
is actually a vertical fall, and because
the car is on a track, it is
not actually freefall at all since a small amount of
friction must be present between the car
wheels and the track
(remember, "freefall" means vertical motion under
the action of only gravity). One way to
determine this is to
measure the time it takes the car to fall only the
vertical distance and compare it to the time
it would
take a true freely-falling body to fall the exact same distance.
Since some friction
on the ride is present, the ride time should
be slight longer. Either way, this ride is a blast!!
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It is really unusual to see these spinning rides like this, because they just don't look
like this at all when you
stand there and watch them! The effect of the camera's
"eye" is much more evident in this image. On this ride,
people are
placed on their bellies on the very outer edge of the ride (as if they are flying) and
complete one
revolution in about 3 seconds or so. Why aren't people
placed near the center on these types of circular rides?
If you think carefully, realize that no matter where two people on
such a ride are put, it will take them both the
same amount of time to complete one circular trip (called a
"period"). However, notice that the person on the
outside travels a
greater distance in one trip (i.e. has a greater circumference), and so that since speed =
circumference/period, the
person travelling
near the outer edge of such a ride is actually moving faster than
someone near the center (where
the circumference is
smaller)! Also, think of it like this; for the ride to be most
exciting to
you, where would you
want to sit, near the center or at the
edge? Near the center, you have such a
small speed that the ride would just
not be exciting
for you, and thus, nearly all such circular rides place people
at the outer edges. As for acceleration (speeding up or
slowing down), one would normally think that people
are NOT accelerating on this ride, since they are travelling at a constant
speed. However, since their direction
is changing, they actually ARE
accelerating! How? Acceleration is the change of velocity as time passes, and
since velocity is a quantity with direction and size, and since a rider's
direction is changing, the rider is accelerating!
Either way, I can't stand
these rides at all because
they make me dizzy and sick!!
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